1. Field of the Invention
This invention relates to a pushbutton switch cover sheet for the key depressing-operation portion of an apparatus, such as a mobile phone, a personal digital assistant (PDA), a car navigation apparatus, or a car audio apparatus.
2. Description of the Related Art
Regarding electronic/electric apparatuses for personal use, a reduction in size and thickness has progressed. Not only is there diversification in function as electronic/electric apparatuses, but also diversification in design is under way. To say nothing of the design of the casing of a mobile phone, there is tough competition in terms of design to achieve product differentiation also regarding a pushbutton switch cover member forming the surface portion of a portable phone. For example, JP 2003-197063 A discloses a resin key top in which a large number of metal foil pieces are laminated on the surface of the resin key top to form a specular gloss layer, thereby attaining a metallic tone. Further, Japanese patent application No. 2004-313857 discloses a pushbutton switch cover sheet using a single thin metal plate. As shown in FIGS. 12 and 13, a pushbutton switch cover sheet (101) as disclosed in Japanese patent application No. 2004-313857 has a structure in which a thin metal plate (102) formed of a single metal plate is firmly attached to a base sheet (103) formed of a rubber-like elastic material, and in which tongue-shaped dividing grooves (104) are formed in the thin metal plate (102) having display portions (105), allowing depression-displacement of each display portion (105).
The pushbutton switch cover sheet (101) disclosed in Japanese patent application No. 2004-313857, in which the key input operating surface is formed by the thin metal plate (102), provides a novel design. However, the thickness of the thin metal plate (102) is as small as 50 μm to 300 μm, which is to be regarded as a problem. That is, in performing key input operation, when a key is depressed with a sharp object such as a fingernail tip or with an excessive force, the surface may be damaged or dented, or the periphery of the dividing grooves (104) or of the display portions (105) may suffer deformation, such as bending.